There are many circuits, particularly voltage level detector circuits, which must discriminate between two voltage levels. A common element of these circuits is that a reference voltage level must be established around which the level detection is founded.
Problems exist, however, when it is understood that the voltage level must be stabilized for temperature changes. Many standard circuits are now available which provide for very stable voltages over wide temperature swings. The problem is that some detector circuits themselves change their internal parameters dependant upon temperature. Thus, in these situations, the reference voltage must also change with respect to temperature to compensate.
A further problem exists in that in some situations, such as a ECL to CMOS logic level conversion circuit, there are different standards to which the reference voltage must be keyed. One of these standards requires the reference voltage to change with temperature while the other standard requires a reference voltage which is constant with respect to temperature changes. It is important to have a reference voltage which is easily converted from one standard to the other with a minimum of difficulty.
This problem is compounded in that, as discussed above, a constant reference voltage can not be used in any event due to changes in the converter circuit.
Thus, a need exists in the art for a voltage reference circuit which changes reference levels based upon temperature gradients with the rate of change very precisely controlled and matched to a given set of circuit components.
A further need exists in the art for such a circuit which can easily be adjusted to have different temperature coefficients to meet different standards.
The reason we needed this voltage reference generator was to drive the ECL to CMOS translator we had designed. We wanted that ECL to CMOS translator to be able to have thresholds, either a standard 100K threshold or a standard 10KH threshold. There are traditionally ECL circuits with these thresholds, and they have reference generators that are well known to produce voltages that allow those circuits to have the standard thresholds. However, because of the nature of this circuit, the threshold reference had to have a much different characteristic in order to get the ECL threshold, and it turned out it had to have some fairly steep temperature coefficients, in other words, the threshold reference had to change significantly as temperature changed in order for example to get the proper thresholds. For example, 100K threshold is -1.32 volts and does not change with temperature or voltage. However, in order to make our ECL to CMOS translator have a threshold that did not change over temperature, this reference voltage actually did have to change over temperature to compensate for other effects in the ECL to CMOS translator. Backing up for a moment, a conventional ECL circuit with 100K threshold has a reference center area that produces a voltage of -1.32 volts, and that voltage does not change over temperature, and it turns out that is the threshold of the circuit. Our ECL to CMOS translator also must have a threshold of -1.32 volts for 100K that does not change over temperature. However, because of the nature of the translator, we cannot feed in a voltage of -1.32 volts. The translator itself affects the threshold, and we have to feed in a different voltage that changes with temperature in order to make the threshold of the circuit be -1.32 volts. The 10KH threshold is also a standard. It is approximately -1.29 volts at room temperature, and its threshold does change as temperature changes. However, the threshold coming into the translator circuit has to change even more significantly in order to have the threshold of the circuit change as 10KH circuits change. There are voltage regulators known as band gap regulators that have been published and are of widespread knowledge of at least 20 years. These type circuits can produce a 10KH or 100K threshold, and there are many papers published on doing exactly that. However, the problem we have here is to produce a voltage with a much different temperature coefficient, and we have never seen anyone need a reference generator whose voltage varies significantly over temperature and at a given known rate. That was the purpose of this circuit.